[FFmpeg-devel] [RFC PATCH] avfilter/video: Protect frame_pool from multi-threads access

[Zhao Zhili]

> On May 10, 2024, at 16:57, Zhao Zhili <quinkblack at foxmail.com> wrote:
> 
> From: Zhao Zhili <zhilizhao at tencent.com>
> 
> Fix crash with
> ./ffplay -f lavfi -i movie=foo.mp4,drawtext=text=bar

This is an RFC because I’m not sure whether it’s a valid use case or not to call
 ff_default_get_video_buffer2 from multiple threads. On one hand, it’s rare used
with multithreads. On the other hand, it can be hidden deep and dangerous.

> ---
> libavfilter/avfilter.c          |  2 ++
> libavfilter/avfilter_internal.h |  2 ++
> libavfilter/video.c             | 14 ++++++++------
> 3 files changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/libavfilter/avfilter.c b/libavfilter/avfilter.c
> index 049e4f62ca..44da809c15 100644
> --- a/libavfilter/avfilter.c
> +++ b/libavfilter/avfilter.c
> @@ -176,6 +176,7 @@ int avfilter_link(AVFilterContext *src, unsigned srcpad,
>     li = av_mallocz(sizeof(*li));
>     if (!li)
>         return AVERROR(ENOMEM);
> +    ff_mutex_init(&li->frame_pool_mutex, NULL);
>     link = &li->l;
> 
>     src->outputs[srcpad] = dst->inputs[dstpad] = link;
> @@ -203,6 +204,7 @@ static void link_free(AVFilterLink **link)
> 
>     ff_framequeue_free(&li->fifo);
>     ff_frame_pool_uninit(&li->frame_pool);
> +    ff_mutex_destroy(&li->frame_pool_mutex);
>     av_channel_layout_uninit(&(*link)->ch_layout);
> 
>     av_freep(link);
> diff --git a/libavfilter/avfilter_internal.h b/libavfilter/avfilter_internal.h
> index 2c31c3e7de..eae3a699c3 100644
> --- a/libavfilter/avfilter_internal.h
> +++ b/libavfilter/avfilter_internal.h
> @@ -27,6 +27,7 @@
> 
> #include <stdint.h>
> 
> +#include "libavutil/thread.h"
> #include "avfilter.h"
> #include "framequeue.h"
> 
> @@ -34,6 +35,7 @@ typedef struct FilterLinkInternal {
>     AVFilterLink l;
> 
>     struct FFFramePool *frame_pool;
> +    AVMutex frame_pool_mutex;
> 
>     /**
>      * Queue of frames waiting to be filtered.
> diff --git a/libavfilter/video.c b/libavfilter/video.c
> index 89d0797ab5..30eba76cbd 100644
> --- a/libavfilter/video.c
> +++ b/libavfilter/video.c
> @@ -70,17 +70,17 @@ AVFrame *ff_default_get_video_buffer2(AVFilterLink *link, int w, int h, int alig
>         return frame;
>     }
> 
> +    ff_mutex_lock(&li->frame_pool_mutex);
>     if (!li->frame_pool) {
>         li->frame_pool = ff_frame_pool_video_init(av_buffer_allocz, w, h,
>                                                   link->format, align);
>         if (!li->frame_pool)
> -            return NULL;
> +            goto out;
>     } else {
>         if (ff_frame_pool_get_video_config(li->frame_pool,
>                                            &pool_width, &pool_height,
> -                                           &pool_format, &pool_align) < 0) {
> -            return NULL;
> -        }
> +                                           &pool_format, &pool_align) < 0)
> +            goto out;
> 
>         if (pool_width != w || pool_height != h ||
>             pool_format != link->format || pool_align != align) {
> @@ -89,18 +89,20 @@ AVFrame *ff_default_get_video_buffer2(AVFilterLink *link, int w, int h, int alig
>             li->frame_pool = ff_frame_pool_video_init(av_buffer_allocz, w, h,
>                                                       link->format, align);
>             if (!li->frame_pool)
> -                return NULL;
> +                goto out;
>         }
>     }
> 
>     frame = ff_frame_pool_get(li->frame_pool);
>     if (!frame)
> -        return NULL;
> +        goto out;
> 
>     frame->sample_aspect_ratio = link->sample_aspect_ratio;
>     frame->colorspace  = link->colorspace;
>     frame->color_range = link->color_range;
> 
> +out:
> +    ff_mutex_unlock(&li->frame_pool_mutex);
>     return frame;
> }
> 
> -- 
> 2.42.0
>